Conventionally, a refrigerator provided with a refrigerant circuit is known, and as a working fluid (refrigerant) for the refrigerator, for example, various fluids are used such as water and a hydrocarbon process gas.
In the refrigerator, the refrigerant evaporated by an evaporator is compressed by a compressor and turns to superheated vapor, and then, the superheated vapor is condensed by a condenser. In the condenser, the superheated vapor is cooled, for example, with cooling water and turns to saturated vapor, and then, the saturated vapor is further cooled and condensed. Hence, the condenser has two main heat-transfer regions: a superheat region where the superheated vapor turns to the saturated vapor and a condensation region where the saturated vapor is condensed. For example, Patent Document 1 cited below discloses a refrigerator having a condensing apparatus in which water is used as a working fluid.
In the above superheat region, a heat-transfer coefficient is smaller than a heat-transfer coefficient in the condensation region. Hence, in the condenser, the area of a heat-transfer surface necessary for the superheat region tends to be larger, thereby requiring that the condenser should be enlarged.
Many refrigerators operate at a degree of superheat of approximately 5 to 7° C. However, in the refrigerator disclosed by Patent Document 1, for example, water is used as a refrigerant to make the degree of superheat higher, requiring a larger heat-transfer surface area in a superheat region. Specifically, in the refrigerator where water is used as the refrigerant, the vapor discharged from a compressor is superheated vapor having a large degree of superheat of approximately 100° C. The heat-transfer coefficient in the superheat region is approximately tens of watts/m2K, which is approximately one-thousandth the heat-transfer coefficient (approximately 10000 W/m2K) in a condensation region. Therefore, in the case where water is used as the refrigerant, the quantity of heat transferred in the superheat region is only several percent of the quantity of heat transferred in the whole of a condenser. Despite this fact, the superheat region needs a heat-transfer surface area equivalent to that of the condensation region, and thereby, the condenser especially tends to be large.